This invention relates to ovenable food containers and more particularly to such containers having a design or graphics ink-printed thereon.
Containers have been developed for the packaging of food, which can also be used to reheat or cook the packaged food in a conventional or microwave oven when the food is to be eaten. Convenience foods may be partially processed or entire meals precooked in containers or food trays made of aluminum, plastic or paperboard. As taught in U.S. Pat. Nos. 3,904,104, 3,924,013 and 3,967,998, containers made from paperboard are generally coated on one or both sides with a water impermeable sealing resin, typically a polyester or polyamide resin.
Food processors rely heavily on packaging esthetics for repeat sales of their products at the retail level. Accordingly, there is a need for a feasible way of applying good quality, durable ink-printed graphics to ovenable food containers, particularly food trays for packaging TV dinners.
Special problems arise when an ovenable food container is to be printed on the side which comes in contact with the food being packaged. Generally speaking, food-grade colors are weak, transparent, do not withstand heating, and are otherwise unsuitable. Prior art approaches have included incorporating a more durable pigment into the water-impermeable sealing layer, as in U.S. Pat. No. 4,343,858, or sandwiching the pigment between layers of polymer as in U.S. Pat. No. 4,327,136. Whatever approach is utilized, the pigment and other ingredients of the printing or coloring composition must be prevented from migrating or coming into contact with the food to be ingested.
Conventional inks inhibit the adhesion of the polyester sealing layer to paperboard. Thus, ink-printing of paperboard with conventional ink formulations followed by coating with polyethylene terephthalate, for example, does not give a satisfactory product when the printed and coated paperboard is formed into a container.